Electric Power Steering Feedback Control for Balanced Reaction Forces
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Solution Overview
Problem
Conventional electric power steering systems face challenges in achieving a balanced steering feel due to independent determination of spring, viscosity, and inertia terms, leading to inappropriate reaction forces that affect driver feedback.
Innovation Solution
An electric power steering system with a control device that calculates a basic control component and reaction force components based on steering torque and state variables, allowing for adjustment of reaction force balance through feedback control and correction of the second reaction force component based on the gradient of the first reaction force component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the spring reaction force is made strong to provide adequate spring support, then the viscosity reaction force becomes weak accordingly, making the driver less likely to feel the viscosity as a change in steering torque
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the viscosity reaction force based on the spring reaction force magnitude. When the spring reaction force is strong, the viscosity reaction force is increased to compensate, ensuring the driver can still perceive viscosity effects. This is achieved by calculating the viscosity reaction force as a function of the spring reaction force, thereby resolving the inverse relationship between these two forces and maintaining balanced steering feedback.
2Force
If the viscosity reaction force is made strong to provide adequate damping, then the spring reaction force becomes weak accordingly, making the driver more strongly feel the viscosity as a change in the steering torque
Solution Approach 1:
The patent uses parameter changes by adjusting the spring reaction force based on the viscosity reaction force magnitude. When the viscosity reaction force is strong, the spring reaction force is increased to compensate, ensuring the driver can still perceive spring support effects. This dynamic parameter adjustment resolves the inverse relationship between spring and viscosity forces, maintaining balanced steering feedback across different operating conditions.
3Device complexity
If the spring term, viscosity term, and inertia term are determined independently to simplify control design, then the balance among these terms cannot be properly adjusted, leading to inappropriate steering reaction forces
Solution Approach 1:
The patent applies parameter changes by making the viscosity and spring reaction forces dependent on each other through calculated relationships. Instead of determining all terms independently, the system calculates the viscosity reaction force based on the spring reaction force magnitude and adjusts accordingly. This interdependent parameter adjustment maintains control design simplicity while achieving proper balance among the terms, resolving the contradiction between design simplicity and steering feel balance.
Data Source
AI summary
Provided is an electric power steering system that achieves a more appropriate steering feel. An ECU of the electric power steering system calculates a basic assist component and a target pinion angle based on at least steering torque. The ECU calculates a correction component for the basic assist component through feedback control in which an actual pinion angle is caused to match the target pinion angle. The ECU calculates an assist command value by adding the correction component to the basic assist component. The ECU corrects a hysteresis controlled variable and a viscosity component according to the rate of change (gradient) in a spring component with respect to a change in absolute value of the target pinion angle. Specifically, the ECU multiplies the hysteresis controlled variable and the viscosity component by gains that have a larger value as the rate of change in spring component increases.